The present invention relates to video signal processing device and method and, more particularly, to a technique which is useful when it is applied to the color reproduction of a color video signal. For instance, the invention can be used in a television receiver, a video reproducing apparatus, or the like.
Recent multi-function television receiver and VCR (video cassette recorder) have two kinds of video signal sources and a function to superimpose a picture (subpicture) of another video signal into a picture (main picture) of one video signal, what is called a PIP (Picture in picture) function. As for the PIP function, for instance, a video signal processing device as disclosed in "Electronic Technique", Vol. May, 1990, pages 42-48, published by The Nikkan Kogyo Shimbun Ltd. is used.
FIG. 16 shows a first constructional example of a PIP system by a conventional video signal processing device. The above PIP system comprises: a main processing system 10 for executing a color process of a video signal forming a main picture; a sub processing system 20 for executing a color process of a video signal forming a subpicture; and a main/subpicture switching portion 30 for superimposing the subpicture into the main picture.
The main processing system 10 comprises: a sync separation circuit 11; a color processing portion 12; a subcarrier generating circuit (APC) 13; a color demodulator 14; and the like. The main processing system 10 separates a chrominance signal C.sub.p, a luminance signal Y.sub.p, a horizontal synchronizing (or sync) signal H.sub.p, and a vertical synchronizing (or sync) signal V.sub.p from the main video signal and generates a subcarrier f.sub.sp of 3.58 MHz on the basis of a color burst signal included in a back porch of the horizontal sync signal.
The sub processing system 20 comprises: a sync separation circuit 21; a color processing portion 22; a subcarrier generating circuit (APC) 23; a color demodulator 24; a subpicture control portion 26; a modulator 27; and the like. The sub processing system 20 separates a chrominance signal C.sub.p, a luminance signal Y.sub.c, a horizontal synchronizing (or sync) signal H.sub.c, and a vertical synchronizing (or sync) signal V.sub.c, from the sub video signal and generates a subcarrier f.sub.sc of 3.58 MHz on the basis of a color burst signal included in a back porch of the horizontal sync signal. The color demodulation is once executed by the subcarrier f.sub.sc on the sub processing system side. Demodulated color difference signals (R-Y) and (B-Y) are converted into predetermined picture sizes together with a luminance signal Y by the subpicture control portion 26. The converted color difference signals (R-Y) and (B-Y) are subsequently modulated into the chrominance signal C.sub.c by the subcarrier f.sub.sp on the main processing system side.
The main/subpicture switching portion 30 replaces parts of the chrominance signal C.sub.p and luminance signal Y.sub.p from the main processing system 10 to the chrominance signal C.sub.c and luminance signal Y.sub.c from the sub processing system 10 by the switching operation. A chrominance signal C which is switched and generated by the main/subpicture switching portion 30 is demodulated into the color difference signals (R-Y) and (B-Y) the subcarrier f.sub.sp on the main processing system side. Consequently, a color synthesized video signal in which the subpicture is superimposed into the main picture, namely, a PIP video signal is obtained.
In the PIP system shown in FIG. 16, the subcarrier generating circuits (APC) 13 and 23 are provided for the main processing system 10 and sub processing system 20, respectively. The chrominance signal C.sub.c on the sub processing system side is once demodulated by the subcarrier f.sub.sc on the sub processing system side and, after that, the demodulated signal is subsequently modulated by the subcarrier f.sub.sc on the main processing system side, thereby converting the subcarrier f.sub.sc of the chrominance signal C.sub.c on the sub side into the subcarrier f.sub.sp on the main side. Due to this, the color reproducing processes of the main side video signal and the sub side video signal which are mutually independent can be correctly executed in the same picture.
FIG. 17 shows a second constructional example of a PIP system according to the conventional video signal processing apparatus. In this system, the main processing system 10 and the sub processing system 20 execute the 3-primary color demodulating processes of RGB by the color demodulators 14 and 24 with matrix circuits 15 and 25, respectively. RGB signals (R.sub.p, G.sub.p, B.sub.p) demodulated on the main side are supplied to the main/subpicture switching portion 30 as signals to be selected. RGB signals (R.sub.c, G.sub.c, and B.sub.c) demodulated on the sub side are converted into predetermined picture sizes by the subpicture control portion 26 and, after that, the converted RGB signals are supplied to the switching portion 30 as the other signals to be selected.
The main/subpicture switching portion 30 replaces parts of the RGB signals (R.sub.p, G.sub.p, B.sub.p) on the main side to the RGB signals (R.sub.c, G.sub.c, B.sub.c) on the sub side by the switching operation. By such a switching and selecting operations, a synthesized image signal in which the subpicture is superimposed into the main picture, namely, a PIP video signal can be obtained as a form of the RGB signals.
In the PIP system shown in FIG. 17, the subcarrier generating circuits (APC) 213 and 23 are respectively provided for the main processing system 10 and the sub processing system 20, the chrominance signal on the main side and the chrominance signal on the sub side are independently demodulated to the RGB signals, and the RGB demodulated signals are synthesized. Since the main side and the sub side use the different signal sources, even when the phases of the subcarriers f.sub.sp and f.sub.sc for demodulation do not correctly coincide, the color reproducing operations of both video signals on the main side and the sub side can be correctly executed in the same picture.
The present inventors, however, have found out that the above technique has the following problems.
That is, in the conventional color signal processing apparatus, as mentioned above, in order to allow the color reproducing operations of the video signals of a plurality of different systems of the signal sources to be correctly executed, it is necessary to provide the subcarrier generating circuit for the color demodulation for every signal system, respectively.
The subcarrier generating circuit, however, must stably continuously generate the subcarrier which is accurately synchronized with a color burst signal inserted in an extremely short interval of the back porch of the horizontal sync signal.
As shown in FIG. 16 or 17, therefore, a quartz-crystal oscillator (Xtal) of a high precision and a capacitor C.sub.x of large capacity are seeded. It is difficult to construct the quartz-crystal oscillator (Xtal) and the capacitor C.sub.x of a large capacity as a semiconductor integrated circuit.
When such a subcarrier generating circuit is provided every signal system, consequently, there occur problems such as enlargement in size of the apparatus due to the difficulty of realization of a semiconductor integrated circuit, high costs due to an increase in number of parts which are externally attached.
In recent years, on the other hand, in a video apparatus such as television receiver, video reproducing apparatus, or the like, in order to improve the picture quality, stabilize the performance, and the like, a digital video signal processing apparatus for digitally processing the color reproduction of the color video signal is often used (for example, refer to "Television Technology", Vol. January, 1990, pages 39-48, published by Densi Gijutsu Shuppan Publishing Ltd.).
In the digital video signal processing apparatus, Y/C separation to separate the luminance signal and the chrominance signals from the video signal, color demodulation to demodulate the color difference signals from the chrominance signals, and the like are executed by digital processes. For the digital processes, the inputted video signal is converted into the digital signal by an A/D converter.
In the conventional apparatus, a clock to decide the sampling timing of the A/D converter and a clock to determine the timing for the digital process such as color demodulation or the like are generated on the basis of the horizontal sync signal of the inputted video signal.
That is, according to the standard color system (NTSC system), the relation between a frequency f.sub.sc of the color burst signal (subcarrier) and a frequency f.sub.h of the horizontal sync signal is defined to be constant (f.sub.sc =455 f.sub.h /2). Therefore, the clock to decide the sampling timing of the A/D converter and the clock to determine the timing for the digital process such as color demodulation or the like can be commonly formed by a PLL (phase locked loop) which oscillates synchronously with the horizontal sync signal of the inputted video signal. When the clock sources of the digital processing systems for A/D conversion, color demodulation, and the like are uniformed by the horizontal sync signal, generation of a jitter due to a deviation of the sampling phase or the like is prevented, so that it is effective for stabilization of the picture or the like.
The present inventors, however, have found out that the above technique has the following problems.
That is, although the conventional digital video signal processing apparatus is effective to the color video signal of the standard system which is specified so as to obtain a predetermined frequency relation (f.sub.sc =455 f.sub.h /2) between the color burst signal and the horizontal sync signal, such an apparatus cannot normally operate for the color video signal of the non-standard system in which the above frequency relation is not always satisfied.
For example, since the video signal which has been received by a television receiver is based on the standard system, the luminance and color information can be accurately and stably reproduced. The video signal derived from a video reproducing apparatus or the like is a non-standard color signal which is slightly deviated from the above frequency relation, so that the color reproduction cannot be correctly executed by the clock synchronized with the horizontal sync signal.
On the other hand, when the sampling clock of the A/D converter is synchronized with the color burst signal in order to accurately perform the color reproduction, a phase error occurs between the sampling timing of the A/D conversion and the horizontal sync signal, so that a jitter in the horizontal direction occurs in the luminance signal.
In the conventional digital video signal processing apparatus, accordingly, two kinds of processing circuits of the digital type and the analog type are provided, the standard color signal is processed by the above digital type, while the non-standard color signal is processed by the conventional analog type.
In this case, however, since the two kinds of digital and analog processing circuits must be provided, the costs of the system rise and a disturbance of the signal such as a skew of picture or the like occurs upon switching of the processing circuits. When the processing circuits are switched, further, it is necessary to judge whether the inputted video signal is the standard or non-standard color signal. There occurs a problem such that a construction to perform such a judgment is fairly complicated and large.